Historically, airbags have been coated with one or more layers of polymeric material to enhance their performance, for example, by preventing the unwanted permeation of air through the fabric and, to a lesser extent, by protecting the fabric from detriment due to exposure to hot gases used to inflate the airbags. Polychloroprene was the polymer of choice in the early development of coated airbags. Subsequently, polychloroprene was almost universally replaced by silicone-based materials.
Newer designs for airbags, particularly those being placed in the sides of passenger compartments, have introduced the requirement that the bags hold pressure longer under use. The requirement of longer air retention times and the use of lower coating levels of silicone polymer have highlighted the effect that a naturally lubricating silicone coating may allow the yarns in the airbag fabric to shift when a sewn seam is stressed. This shifting may lead to leakage of the inflating gas through pores formed from the shifting yarns.
In the past, extended pressure retention times have been achieved by applying a first layer of gas-retaining polymer (such as a silicone-containing polymer) to the fabric surface and then applying a second, protective layer over the first layer. The second, protective layer prevents the airbag coating from sticking to itself when folded and stored (a condition known as “blocking”) and also protects the first, gas-retaining layer from damage due to aging, abrasion, and the like. In most situations, the second layer also helps to minimize the burn rate of the airbag to satisfy burn test requirements as mandated by Federal Motor Vehicle Safety Standard (FMVSS) 302.
Various coating systems have been advocated combining silicone with different polymers in the same polymer network. By way of example, such silicone-based coating systems are described in U.S. Pat. Nos. 6,348,543; 6,468,929; 6,545,092; 6,846,004; and U.S. Patent Application Publication No. 2005-0100692 all to Parker and all of which are hereby incorporated by reference as if fully set forth herein.
Various multi-layered coating systems have also been advocated. In this regard, exemplary multi-layer systems are set forth in U.S. Pat. Nos. 6,239,046; 6,641,686; 6,734,123; and 6,770,578 all to Veiga and 6,177,365 and 6,177,366 to Li all of which are hereby incorporated by reference as if fully set forth herein.
Airbag manufacturers have used these and other solutions to address the multiple problems associated with forming a suitable coating composition. Specifically, the airbag coating is required to provide the necessary gas retention properties to the airbag. It is also desirable that the coating impart flame retardance to the airbag. In this regard, flame retardance has typically been achieved by incorporating flame retardant additives into the top layer(s) of a multi-layered coating, since the incorporation of flame retardant additives into the fabric-contacting layer may impair gas retention. Another desirable characteristic is the avoidance of so called “blocking” in which the coating compositions tend to stick to themselves when the bags are folded and stored over long periods of time. Finally, another desirable feature is the need for the airbag coating to be stable to aging, meaning that the coating will not degrade over time and in extreme conditions of heat and/or humidity.
As best understood, single coating layers have been generally deficient in meeting these various problems. Thus, the use of multi-layered coatings has gained relatively broad acceptance. The urethane-based coating composition of the present disclosure may be used as a monolithic coating layer for airbags with performance characteristics comparable to those of the prior multi-layered coatings. Accordingly, the disclosure provides a useful advancement over the prior art.